1. Field of the Invention
This invention relates to a novel self-bonding magnet wire, and more particularly, to a self-bonding magnet wire having high refrigerant resistance and exhibiting high bond strength at high temperatures.
2. Description of the Prior Art
A recent trend in the manufacture of electric appliances is to omit or simplify the varnish impregnating step by using a "self-bonding magnet wire" which comprises an insulated conductor having an outer coating of a heat-bonding layer. The heat-bonding layer is conventionally made of a poly(vinyl butyral)resin, co-polyamide resin, phenoxy resin or polysulfone resin. Common applications of such self-bonding magnet wire include use in deflecting yoke coils for television sets, in voice coils for speakers or microphones, as well as in various transformers and motors. And the demand for the self-bonding magnet wire in hermetic motors and other applications which require refrigerant- and heat-resistance is increasing.
However, self bonding magnet wire using known bonding materials is poor in resistance to refrigerant and/or heat, and hence, is not very suitable for use in hermetic motors and other applications which require refrigerant- and heat-resistance electric wires. Heat-bonding layers composed of poly(vinyl butyral)resin, copolyamide resin or phenoxy resin are low in both heat resistance and refrigerant resistance, whereas those made of the heat-resistant polysulfone resin are not satisfactory in refrigerant resistance. The self-bonding layer of the conventional self-bonding magnet wire using these materials is dissolved out in a refrigerant such as Freon.RTM. R-12 or Freon.RTM. R-22 (trademark) and fails to achieve the desired bonding function. Furthermore, an insoluble ingredient extracted with a refrigerant can clog the opening of the compressor valve or a refrigerant expansion valve in a refrigerator, to reduce the refrigerating capacity of the refrigerator. In addition, if the motor is started in spite of voltage drop or abnormal operation (e.g., when the compressor is started immediately after its shutdown) involving a locked rotor, an overload on the stator causes a rapid increase in the temperature of the coil, and an electric wire using the conventional bonding material discolors or blisters and its electrical characteristics are reduced to such an extent that layer shorting, i.e., short-circuiting between magnet wires, occurs. Under normal operation, the motor is run in the refrigerant at from 80.degree. to 100.degree. C., but a self-bonding layer made of the conventional bonding material becomes low in bond strength if it is immersed in the refrigerant, and as a result, the coil may be deformed.